1. Technical Field
This invention relates to heat-curing reactive compositions based on natural and/or synthetic elastomers containing olefinic double bonds and vulcanizing agents which have acoustic damping properties in the vulcanized state. The invention also relates to a process for the production of these compositions and to their use as adhesives, sealing compounds and coatings.
2. Background of the Invention
Nowadays, motor vehicles, machines and appliances are made almost exclusively from very thin metal sheets. Mechanically moving parts or running engines unavoidably cause these thin sheets to vibratexe2x80x94often in the hearing range of the human ear. These vibrations are propagated in the form of mechanical vibration throughout the entire vehicle, machine or appliance and can be radiated into the air as troublesome noise at remote places. Accordingly, to reduce sound radiation and vibration damping, these sheets are provided with noise-damping coatings, so-called anti-vibration coatings, especially in automobile manufacture and in the manufacture of domestic appliances.
The conventional procedure adopted for this purpose is to extrude mixtures of fillers of high specific gravity and bitumen to form films from which the corresponding shaped parts are then stamped or cut. These films are then bonded to the metal sheets in question, optionally having to be adapted to the shape thereof by heating. Although these bitumen films are still frequently used by virtue of their low material price, they are extremely brittle and tend to flake off the metal sheet, particularly at low temperatures. The frequently proposed additions of elastomers also produce only a slight improvement which is inadequate for many applications. In addition, preformed bitumen parts cannot be applied to intricately shaped or awkwardly situated sheet metal parts of machines or vehicles, for example the inside surfaces of doors. Another disadvantage is that, in many cases, several stamped parts are required for a single vehicle or appliance and, accordingly, have to be expensively stored in appropriate numbers.
Accordingly, attempts have been made to eliminate the disadvantages of bitumen films by using other polymer systems. For example, filler-containing aqueous polymer dispersions of polyvinyl acetate or ethylene/vinyl acetate copolymers have been developed and can be sprayed onto the sheet metal parts in the necessary layer thickness. Unfortunately, systems such as these are a disadvantage for use on an industrial scale where large numbers are always involved because the water cannot be removed quickly enough from the layer applied by spraying, particularly in considerable. layer thicknesses. Another disadvantage of these conventional noise-damping methods is that the materials in question serve the sole purpose of damping noise.
In the manufacture of vehicles, machines and appliances, efforts are now being made to simplify the complexity of the production processes and hence to reduce manufacturing costs.
In addition, adhesives, sealing compounds and coatings are used in the manufacture of vehicles, machines and appliances. Hitherto, the adhesives and/or sealing compounds have been mainly selected for their primary properties:
strength, i.e. shear strength, peel strength
elongation at break, flexibility
resistance to ageing
simple handling.
In the case of coatings, particularly underseal coatings, abrasion resistance is another selection criterion.
Numerous efforts have been made to reduce the complexity of the manufacture of vehicles, machines and appliances and hence to reduce manufacturing costs. Accordingly, there is a need for xe2x80x9cmultifunctional productsxe2x80x9d, i.e. for example there is a need for adhesives, sealing compounds and/or coatings which, besides their main function, are capable of solving additional problems.
EP-A-358 598 and DE-A-3 444 863 describe plastisol formulations which perform the dual function of undersealing (protection against abrasion) and acoustic damping. DE-A-4 013 318 describes a two-layer undersealing compound which performs the function of undersealing and absorbing the noise emanating from impacting particles (stones, chippings, water, etc.). Although these products/processes perform the dual function of undersealing and noise damping extremely satisfactorily, there is mainly a need to combine the function of an adhesive and/or sealing compound with noise damping. This is particularly desirable for those parts of an automobile, a machine or an appliance which do not require any protection against abrasion, such as for example the trunk lid, the hood, the doors or the end wall of a vehicle.
Adhesives and sealing compounds for these parts are normally applied at an early stage of the production process known as xe2x80x9cshell constructionxe2x80x9d. The metal sheets used are covered with anti-corrosion oils and drawing oils in thicknesses of several grams per m2, so that the adhesive/sealing compound used has to be able to absorb these oils. Although plastisols, particularly PVC plastisols, are used in shell construction, the plastisols disclosed in EP-A-358 598 or DE-A-3 444 863 are not suitable as adhesives/sealing compounds for shell construction. Plastisol formulations which have been specifically developed for shell construction have only minimal noise-damping properties, if any.
Another group of adhesive/sealing compounds suitable for use in shell construction is based on rubbers, more particularly vulcanizable compositions based on 1,4-polybutadienes and/or 1,4-polyisoprenes. These compositions preferably contain liquid polydienes of low molecular weight, sulfur and optionally accelerators for sulfur vulcanization. In addition, these compositions may contain high molecular weight, so-called solid rubber, both the liquid polydienes and/or the solid rubber optionally containing functional groups such as, for example, hydroxyl groups, carboxyl groups, anhydride groups or epoxy groups. This group of rubber-based adhesive/sealing compounds is described in a number of patent applications, for example EP-A-97 394, EP-A-309 903, EP-A-309 904, DE-A-3 834 818, DE-A-4 120 502, DE-A-4 122 849, EP-A-181 441 and EP-A-356 715.
It is apparent from DE-A-4 122 849 that the object of bonding metal sheets in the construction of automobile shells is inter alia to damp any vibration occurring. Although the document in question does not provide any particulars in this regard, it may be assumed that the vibrations in question are low-frequency vibrations outside the range of hearing of the human ear, such as for example the vibrations of hood trunk lids and doors where they have no suitable reinforcing frames (xe2x80x9cantiflutter adhesivesxe2x80x9d).
EP-A-181 441 describes two-component, thermally crosslinkable compositions and processes for the production of cold-crosslinking compositions, one binder containing hydroxyl groups and the second binder containing carboxylic acid groups or anhydride groups. The two components have to be mixed immediately on application, curing taking place either by heating with ester formation between the hydroxyl groups and the carboxylic acid groups or in the cold, in which case catalysts have to be added. According to the document in question, the compositions may be used inter alia as vibration damping compositions or noise damping compositions. The document does not provide any further particulars, particularly in regard to the effectiveness of damping or the substrates which are to be damped.
Hitherto unpublished European patent application 93 120 384.8 describes the use of 3,4-polyisoprene in combination with other curable or non-curable liquid and/or solid rubbers and the use of these compositions for one-component, hot-vulcanizable adhesive/sealing compounds with acoustic damping properties.
It has been found that one-component, heat-curing (vulcanizable) adhesive/sealing compounds based on liquid rubbers and optionally solid rubbers can be modified in such a way that there is no need to use the difficult-to-obtain 3,4-polyisoprene, in spite of which extremely effective acoustic damping is obtained with these compositions.
In the context of the present invention, acoustic damping or vibration damping is understood to be the damping of mechanical vibration which is known to reduce the vibration of sheet metal constructions.